A fairly basic security slip has showed just how far the British police are preparing to go to make sure Julian Assange doesn't leaving the UK without getting his collar felt.

Police plan caught by snapper (click to enlarge) Credit: PA

"Action required – Assange to be arrested under all circumstances," reads a handwritten briefing note photographed in the hands of one of the officers surrounding the Ecuadorian embassy. The note says Assange is to be arrested if he leaves the embassy in the company of another diplomat or if the Ecuadorians try and smuggle him out in the diplomatic bag.

The police briefing note also warns that there may be an attempt at disruption to aid Assange's escape, possibly by the protestors who are at the embassy. The note references SS10, which may be a misspelling of SO10, the Metropolitan Police's covert operations group, and SS20, the forces' counter-terrorism protective security command.

Checking the diplomatic bag to the embassy might seem nonsensical, summoning up images of Assange contorting himself into a piece of luggage, but diplomatically protected luggage can be anything up to and including a shipping container and they've carried people before.

In 1985 relations between the Nigerian government and the British were strained when the former Nigerian transport minister Umaru Dikko was abducted in London, drugged and found in diplomatic freight by police. In that case the authorities were able to inspect the crate Dikko had been stuffed into because the diplomatic paperwork on the flight had been incorrectly filed.

When it comes to its own diplomatic materials, however, the British government takes a harder line. It issued a strong protest when the sanctity of its own diplomatic bag was violated by Zimbabwean authorities in 2000.

The Ecuadorian government has also had its own problems in this area. In February the Italian authorities found 40kg of cocaine in diplomatic mail. The Ecuadorians allowed the search that discovered the drugs and announced a full investigation.

So for the moment the stand-off continues. Assange seems safe from extradition within the embassy grounds and has a long time to go before he becomes a long-standing occupant. The all-time winner of the embassy house-guest award is still held by Catholic cardinal József Mindszenty, who lived at the US Embassy in Budapest from 1956 to 1971. ®